Thermal controlled arming device for a mine



Nov. 29, 1960 J. F. TOOMEY ETAL Filed March 8, 1944 2,961,958 THERMALCONTROLLED ARM'ING DEVICE FOR A MINE 4 Sheets-Sheet 1 Fl &

Nov. 29, 1960 J. F. TOOMEY ETAL 2,961,958

THERMAL CONTROLLED ARMING DEVICE FOR A MINE 1- Sheets-Sheet 2 FiledMarch 8, 1944 LOAD Nov. 29, 19 60 J. F. TOOMEY ETAL 2,961,958

THERMAL CONTROLLED ARMING DEVICE FOR A MINE Filed March 8, 1944 4Sheets-Sheet 3 2T 43 W WWW I e?! i Nov. 29, 1960 J. F. TOOMEY EI'ALTHERMAL CONTROLLED ARMING DEVICE FOR A MINE Filed March 8, 1944 4Sheets-Sheet 4 MINE FIRING CONTROL MECHANISM P MINE FIRING l l l CONTROLMECHANISM I 9 k MINE n I 7 FIRING r 8 CONTROL MECHANISM THERMALCONTROLLED ARMING DEVICE FOR A MINE John F. Toomey, Floral Park, N .Y.,and Ellis M. Brown, Dallas, Tex.

Filed Mar. 8, 1944, Ser. No. 525,610

Claims. (Cl. 102-16) (Granted under Title 35, US. Code (1952), see. 266)a fusible alloy and thereby release an actuating member.

The device of the present invention is particularly adapted for use incontrolling the firing mechanism of a mine by selective control of theelectrical circuits connected thereto when a predetermined period oftime has elapsed after the mine has been launched thereby to arm themine in time delayed relation with respect to the launching thereof andto render the mine harmless or sterile, if desired, at the expiration ofa substantially greater period of time after the mine has been launchedin which there is no possibility of prematurely operating the contactactuating mechanism as the result of the violent shock received when themine is planted from an aircraft in flight.

In arrangements heretofore proposed in which a relay having a movablemagnetically responsive element is employed for arming a mine, or themine is armed as the contacts of an arming clock are closed, the shockor excessive vibration caused by the impact of the mine against thesurface of a target area may be sufiicient to operate the contactactuating mechanism or momentarily operate the arming clock contacts, asthe case may be, and thus prematurely arm and fire the mine.

In the arrangement of the present invention, the contact actuatingmechanism comprises a movable element having means operatively connectedthereto for yieldably urging the movable element toward an operatedposition thereof, the element, however, being normally restrained frommoving into the operated position by a sleeve or collar releasablybonded thereto by a fusible alloy whereby the movable element is lockedin an initial or unoperated position at all times until the alloy hasmelted or softened sufficiently to permit relative movement of themovable element with respect to the collar. The device also includes aheater element or heater disposed adjacent the aforesaid fusible alloyand adapted to destroy the bond between the collar and the movableelement by melting the fusible element in response to a flow of currentthrough the heater. When this occurs, the contact actuating mechanism ismoved to the operated position by any means suitable for the purposesuch, for example, as a resilient spring and thereby operate the contactelements associated with the device, the circuit to the heater beinginvariably interrupted concurrently therewith.

One of the objects of the present invention is the pro vision of a newand improved circuit controlling device in which means are provided forpreventing the operation of the contact actuating mechanism as a violentshock is received.

Another object is the provision of a new and improved thermal controlleddevice adapted to withstand a severe 2,961,958 Patented Nov. 29, 1960shock or blow without being operated thereby and in which means areprovided for actuating a mechanism operatively connected thereto inresponse to a predetermined flow of current received by the device.

Another object is to provide a thermal controlled relay in which meansare provided for preventing movement of the contact actuating mechanismfrom an initial locked position until the thermal element has beenheated to a predetermined temperature.

Another object is to provide a normally locked thermal relay in whichthe relay actuating element is prevented from moving from an initiallocked position until the thermal element has been heated to apredetermined temperature and in which the relay is operated without anadditional increase in the temperature of the thermal element.

Another object is the provision of a thermal relay having an actuatingelement normally locked in an initial position in which the actuatingelement is unlocked only in response to a predetermined fiow of currentto a heater and in which means are provided for discontinuing the flowof current to the heater as the relay operates.

A further object is to provide a new and improved thermal controlleddevice which is economical to manufacture, compact in structure,reliable in operation, and which is suitable for a large variety ofuses.

Still other objects, advantages, and improvements will be apparent fromthe following description taken in connection with the accompanyingdrawings of which:

Fig. l is a top plan view of a thermal relay in accordance with thepresent invention;

Fig. 2 is an end view of the device of Fig. 1;

Fig. 3 is a view somewhat enlarged taken along the line 3-3 of Fig. 1and showing the device in an unoperated condition;

Fig. 4 is a view similar to Fig. 3 showing the device in an operatedcondition;

Fig. 5 is an enlarged sectional view taken substantially along the line5-5 of Fig. 1;

Fig. 6 illustrates in diagrammatic form one of the many uses of thedevice;

Fig. 7 is a top plan view of an alternative form of the device;

Fig. 8 is an end view of the device of Fig. 7;

Fig. 9 is an enlarged sectional View taken along the line 9-9 of Fig. 7and showing the device in an unoperated condition;

Fig. 10 is a fragmentary view partly in section showing the device ofFig. 9 in an operated condition;

Fig. 11 illustrates in diagrammatic form a circuit arrangement for thedevice of Fig. 7 suitable for sterilizing the firing control mechanismof a mine;

Fig. 12 illustrates in diagrammatic form a circuit arrangement for thedevice of Fig. 7 suitable for arming a mine; and, i

Fig. 13 illustrates diagrammatically still another circuit arrangementin which the device of Fig. 7 is employed to close a plurality of armingcircuits and in part the firing circuit for a mine.

Referring now to the drawings for a more complete understanding of theinvention, and more particularly to Figs. 1 to 5 thereof, there is shownthereon a thermal relay indicated generally by the numeral 19 comprisinga casing 11 composed of material suitable for the purpose such, forexample, as Bakelite or Lucite and provided with a cylindrical bore 12therein. The casing is also threaded as at 13 thereby to receive a cap14 and secure the cap to the casing. The cap is preferably knurled at 15and provided with a shoulder 16 thereby to clamp a terminal connection17 to the cap as the cap is secured to the casing. The cap is providedwith a plunger 18 slideably arranged therein and continuously urgedinwardly by a spring 19 in registered engagement with the shoulder 21formed on the plunger and with the bottom of a well 22 within the cap.The plunger is also provided with a washer or stop member 23 secured tothe outer end portion thereof and adapted to arrest the inward movementof the plunger by engagement with the cap as the relay operates.

The cap is also provided with a cylindrical recess 24 within which isarranged a spring 25, the spring being in registered engagement with athrust plate or washer 26 and adapted to move the washer along thecylindrical recess 24 as the relay operates. The washer is composed ofsuitable insulating material such, for example, as Bakelite.

The opposite end of the casing 11 is provided with a thimble or sleeve27 having flanged portions 28 and 29 adapted to secure the sleeve to thecasing, a terminal member 31 being arranged between the flanged portion29 and the casing. There is slideably arranged within the sleeve 27 aplunger or rod 32 having a cylindrical member 33 secured thereto, thecylindrical member being composed of insulating material suitable forthe purpose such, for example, as molded Bakelite, the plunger 32 beingpreferably formed as at 34 and 35 to receive the molded Bakelite andstrengthen the connection therebetween. The cylindrical member 33includes a tapered portion 36 about which is formed a cap 37 composed ofmetal and having a projecting cylindrical portion 38 extending withinthe thrust plate 26 and adapted to engage the inner end of the plunger18, a washer 39 being arranged between the end of the plunger 32 and thecap 37 to maintain the plunger electrically insulated from the cap. Thecap 37 is also provided with a shoulder 41 in abutting relation with thethrust plate.

The plunger 32 is also provided with a sleeve 42 slideably arrangedthereon and releasably bonded thereto by a fusible alloy 43 composed oflow fusing metals such as lead, tin and antimony in such proportions aswill allow the alloy to be melted at a temperature of substantially 210degrees Fahrenheit and adapted to be melted in response to heat receivedfrom a heat coil or heater 44 disposed about the sleeve 42. The heatercomprises a number of turns of resistance wire, one end of the wirebeing connected at 45 to the sleeve 42 and the other end connected as bythe flexible conductor 46 to the cap 37 to which the end of theconductor is secured as by soldering the parts together. The cylindricalmember 33 is provided with a slotted portion 47 within which theconductor 46 is arranged thereby to facilitate movement of the cap 37 asthe relay operates. The plunger 32 is thus locked in an initial positionby the sleeve 42 by reason of the engagement of one end of the sleevewith the flanged portion 28 of the thimble 27, and with the outer end ofthe plunger substantially flush with the outer surface of the casing 11.

The casing 11 is attached to a support 48 as by the screws 49, thesupport having a bent up portion 51 to which is attached as by thescrews 52 a spring pile-up indicated generally by the numeral 53, thepile-up comprising a pair of movable contact springs 54 connectedtogether as by the insulating member 55 and adapted to engage thecontact springs 56 as the member 55 is moved to the operated position bythe plunger 32. The contact springs 54 and 56 are electrically insulatedfrom each other and from the support 48 by spacing members 57. Thecasing 11 is also provided with a pair of bores 58 adapted to receivethe bolts 59 and thereby attach the device to a mounting plate or base61, Fig. 5.

The device is adapted to a variety of uses such, for example, asconnecting a load to a source of electrical power in response to theclosure of a control key, such an arrangement being shown in Fig. 6 inwhich the device is adapted to be connected to a battery B when theswitch S is moved to a closed position. When this occurs, the heater 44is energized by current from the battery B thereby melting the fusiblealloy and releasing the plunger 32. The plunger is now actuated by thespring 25 into engagement with the member 55 thereby moving the contactsprings 54 connected thereto into engagement with the contact springs 56and concurrently therewith interrupting the circuit to the heating coilat 62, corresponding to the point of engagement of the plunger 18 withthe end of the cap 37. As the contact springs 54 engage the contactsprings 56 the load is connected to the battery B. Whereas in Fig. 6 theload is shown in diagrammatic form, it will, of course, be understoodthat this is by way of illustration only as the load may comprisevarious control circuits and mechanisms therefor such, for example, asthe mechanisms and circuits employed with mines in which the detonationof the mine is accomplished by closing a firing circuit to anelectroresponsive detonating device.

On Figs. 7 to 10 is shown an alternative form of the device in which theplunger 32 is preferably set back slightly from the surface of thecasing 11. The spring pile-up indicated generally by the numeral 63,however, comprises two contact elements 64 and 65 adapted to be moved toan operated position by the plunger 32 by reason of the provision of aspacing member 66 of suitable insulating material disposed between thecontact springs. The contact spring 64 is provided with a contactelement 67 adapted to be engaged by the plunger 32 and establish anelectrical circuit therebetween as the relay operates. As the plunger 32moves to the operated position, the contact spring 65 is moved intoengagement with the contact element 68 and engages the contact element68 with sufficient force to cause the element 68 to be moved intoengagement with and be arrested by the stop member 69. The contactsprings 64, 65, 68 and the stop member 69 are normally electricallyinsulated from one another and from the support 48 by reason of theprovision of the insulating spacing members 71.

The relay of Fig. 7 is arranged such that the contact spring 64 isprevented from being brought into engagement with the plunger 32 priorto the release of the plunger from the initial locked position thereofby reason of the provision of a relatively small recessed portion 72within the casing 11 within which the bearing support for the plunger 32is arranged. As illustrated in dashed outline on Fig. 7, the spring 64is adapted to be arrested by the casing 11 as the spring is set intovibration or suddenly moved from an initial position as the result of aviolent shock received before the spring has moved through a distancesufficient to engage the rod 32.

The manner in which the device of Fig. 7 may 'be employed for renderinga mine harmless when a predetermined period of time has elapsed afterthe mine has been launched, is illustrated on Fig. 11 of the drawings inWhich a mine firing control mechanism is adapted to be operativelyconnected to a source of electrical power BA in response to the closingof the contacts of an arming clock AC, means in the firing controlmechanism being provided for closing a firing circuit to the detonator Din response to the movement of a vessel within the eifectivc zone ofdestruction of the mine. In the event, however, that the detonator isnot operated within a predetermined period of time, the contacts of asterilizing clock SC are closed thereby completing a circuit from thebattery BA to the heat coil 44 of the thermal relay. When the fusiblealloy has become heated sufliciently to disengage the plunger 32 fromthe sleeve 42, the plunger is moved by the spring 25 into electricalengagement with the contact spring 64 thereby short circuiting thebattery BA. Concurrently therewith the spring 65 is moved intoengagement with the contact element 68 thereby short circuiting thedetonator D. The mine is thus rendered harmless or sterile bydischarging the battery, accidental or incidental firing of the mineconcurrently therewith being prevented by the short circuit across thedetonating device D as the result of the engagement of contact spring 65with the contact element 68. As the rod 32 moves to the operatedposition thereof the circuit to the heater coil is interrupted at 62 bythe cap 37 moving out of engagement with the end of the plunger 18.

On Fig. 12 is shown an arrangement in which the device of Fig. 7 isemployed for arming a mine in response to the operation of an armingclock AC. When the contacts of the arming clock close, the heater 44isenergized thereby causing the plunger 32 to be released and moved intoengagement with contact spring 64. Contact spring 64 is electricallyconnected to contact spring 65, and as contact spring 65, therefore,engages contact element 68, negative battery is applied to conductor 73and concurrently therewith negative battery is also applied to conductor74 extending to the mine firing control mechanism to which positivebattery is connected as by the conductor 75. The mine is now armed andin readiness to fire the detonator D in response to the movement of avessel within the vicinity of the mine. As the plunger 32 moves to theoperated position, the current through the heater coil is discontinuedby reason of the interruption of the heater circuit at 62 thereof.

Still another arrangement for arming a mine is shown on Fig. 13 in whichthe thermal device is employed to close an arming circuit andconcurrently therewith to close in part the firing circuit to thedetonating device D in response to the operation of the contacts of thearming clock AC. When the heater coil 44 has been energized sufficientlyto release the plunger 32, negative potential from the battery BA isapplied by way of the plunger 32 and contact element 64 to conductor 76extending to the mine firing control mechanism, the positive terminal ofthe battery being connected to the mine firing control mechanism by wayof conductor 77. As contact spring 65 moves into engagement with contactelement 68, conductor 78 is brought into electrical connection withconductor 79 extending to the detonator D, from whence the circuit iscontinued by way of conductor 81 to the mine firing control mechanismthereby closing in part a firing circuit to the detonator D as thethermal relay operates.

Whereas in Figs. 1 and 7 respectively there is disclosed a thermal relayhaving two pairs of normally open contacts adapted to be closed as therelay operates, it will be understood that this is by way of exampleonly as various other combinations of contacts and various other springpile-ups including pile-ups having one or more pairs of normally closedcontacts may be employed with the thermal control release mechanismdisclosed herein for various purposes in which a control connection or aplurality of control connections are made effective in response to apredetermined flow of current through the heater element. Furthermore,the contact control ele ments may be operated in predetermined timedelayed relation over a considerable range of time intervals inaccordance with the selected resistance of the heater circuit includingthe heater element and the voltage applied thereto. In any case,however, the plunger rod is prevented from moving from an initial lockedposition until sufficient heat has been applied to a fusible alloy tocause the fusible alloy to soften and release a locking member fusedthereto. When this occurs, the plunger is. moved quickly and positivelyby a source of energy stored within the device to the operated positionthereof without the necessity of additionally heating the fusible alloy.As the plunger moves to the operated position, the contact elements areactuated thereby and the flow of current to the heater coil isinvariably interrupted.

An arrangement is thus provided in which, by employing a fusible alloybonded to the actuating element in the manner disclosed, the actuatingelement is prevented from being moved from an initial locked position asthe result of a shock received, the actuating element remaining lockeduntil the fusible alloy has softened sufficiently to release the bond inresponse to a predetermined degree of heat applied thereto by theheater.

While the invention has been described in connection with two mechanismswhich are adapted for the uses set forth in the description, it is to beunderstood that the reference to such uses shall not limit the inventionthereto and that various changes may be made in the mechanism employedwithin the principles of this invention, and that any words ofdescription that may be imported to the claims from the specificationare not to be considered as words of limitation.

The invention herein described and claimed may be manufactured and usedby or for the Government of the United States of America forgovernmental purposes without payment of any royalties thereon ortherefor.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. In a device of the character disclosed for arming a mine, incombination, a source of electrical power, a thermal element on saiddevice, circuit means including a pair of normally closed contacts forconnecting said element to said source of power, locking means withinsaid thermal element and adapted to be heated thereby, an actuatingmember on said device and movable from an initial cocked position to areleased position, said normally closed contacts being arranged to beoperated by said actuating member during initial movement thereofthereby to deenergize said thermal element, means for moving saidactuating member, means fusibly bonded to the actuating member and tothe locking means for releasably locking the actuating member in saidinitial position, a mine firing control mechanism, and means on saiddevice for connecting the mine firing mechanism to said source of powerduring movement of the actuating member from said initial position tothe released position.

2. A thermal controlled arming device for a mine having an actuatingmember movable from an initial locked position to a released position,means for moving the actuating member, means including a fusible elementbonded to the actuating member for releasably locking the actuatingmember in said initial position, a heat coil adapted to increase thetemperature of said fusible element sufiiciently to release theactuating member from said locking means, a source of electrical power,an anning circuit for connecting the heat coil to said source of power,a pair of normally closed contacts in said arming circuit adapted to bedisengaged during the movement of the actuating member from said initialposition to the released position thereby to disconnect the heat coilfrom the source of power when the actuating member has been released, amine firing mechanism, and means controlled by the actuating member forconnecting the mine firing mechanism to said source of power as theactuating member moves into said released position.

3. In a thermal controlled arming device for a mine, a control elementadapted to be moved from an initial cocked position to a final position,means for actuating said control element, means including a fusiblealloy bonded to the control element for releasably locking the controlelement in said initial position, an electroresponsive heater adapted tomelt the fusible alloy sufficiently to release the control element fromsaid locking means, a source of electrical power, circuit meansincluding a pair of normally closed contacts for energizing said heaterfrom said source, said normally closed contacts being arranged to beopened by said control element during initial movement thereof therebyto deenergize said heater, an arming circuit for connecting the sourceof power to said heater and to the control element, a mine firingmechanism having a plurality of control circuits connected thereto, acontact element adapted to be engaged by said control element during themovement of the control element into said final position and therebyconnect one of said control circuits to the source of power, and meansincluding an additional contact element on said device for connectinganother of the control circuits to said source of power as the controlelement moves into said final position.

4. In a system for a mine having an explosive charge therein, anelectroresponsive device for detonating said charge, a firing controlmechanism, a firing circuit connected to said detonating device andadapted to be closed by said firing control mechanism, an arming circuitfor the firing control mechanism, a source of electrical power, athermal device having an electrical heater controlled element adapted tobe connected to said source of electrical power, means for closing saidarming circuit in response to a predetermined flow of current applied tosaid heater element by the source of electrical power, and means on saidthermal controlled device for closing in part said firing circuit inresponse to said predetermined flow of current.

5. In a system for a mine having an explosive charge therein, anelectroresponsive detonator adapted to fire the charge, a firing controlmechanism, a firing circuit for said detonator adapted to be closed bythe firing control mechanism, a source of electrical power, a thermalcontrolled disarming device having an actuating element movable from aninitial locked position to a released position, means adapted to movesaid actuating element, means including a fusible alloy bonded to theactuating element for releasably locking the actuating element in saidinitial position, means including a heater adapted to melt the fusiblealloy suificiently to release the actuating element from said lockingmeans in response to a predetermined flow of current from said source ofpower, means for connecting the heater in circuit with the source ofelectrical power when a predetermined period of time has elapsed afterthe mine has been planted, a normally closed switch in said heatercircuit arranged to be opened by said actuating element during theinitial movement thereof, means on said disarming device for shortcircuiting the source of electrical power as the actuating element movesinto said released position, and contact closing means on the disarmingdevice operatively connected to said firing circuit and adapted to shortcircuit the detonator when the actuating element is in said releasedposition.

6. A thermal control device of the character disclosed comprising, incombination, a tube of non-conducting material having an inturned flangeforming an axial opening at one end thereof, a sleeve of conductingmaterial disposed within said opening and secured to said flange, aconductor ring secured between said sleeve and flange, an actuating rodarranged for sliding movement within said sleeve from an initial lockedposition within said tube to a moved position extending outwardly ofsaid flange, a tube of conducting material sleeved about said rod andarranged in abutting engagement with said sleeve, a fusible bond forreleasably locking said rod to said conducting tube with the rodarranged in said initial position thereof, an electric heat coil mountedon said conducting tube in heat transfer relation therewith and havingone end of the coil electrically connected thereto, a piston connectedto the other end of said rod and arranged for sliding movement withinsaid non-conducting tube, a contact carried by said piston in axialalignment with said rod and electrically connected to the other end ofsaid coil, a conducting cap secured to the other end of saidnon-conducting tube and having an inwardly extending hub portion, acontact ring secured between said cap and said non-conducting tube, saidhub portion having a central bore in axial alignment withisaid rod, acontact rod arranged for sliding movement within said central bore andinitially arranged with one end thereof in electrical engagement withsaid piston contact thereby to complete a circuit for energizing saidcoil when said contact rings are connected to a source of electricalenergy, a coil spring sleeved about said hub portion between said pistonand said cap for moving said rod to said moved position thereof when thecoil has been energized sufliciently to diffuse and break said bond, astop member carried by the other end of said contact rod and arranged toengage said cap upon limited follow-up movement of the contact rod withrespect to said actuating rod, and a coil spring sleeved on said contactrod and arranged to yieldably urge the contact rod into said follow-upengagement with said piston contact whereby energization of the coil ismaintained until said stop member engages the cap.

7. A thermal control device of the character disclosed comprising, incombination, a non-conducting tube, an actuating rod arranged forsliding movement within one end of said tube for movement from aninitial locked position to a moved position, means including a fusiblebond for releasably locking said rod in said initial locked position, aconducting sleeve on said rod, a heater coil mounted on said sleeve inheat transfer relation with respect thereto for breaking said bond whenthe coil is energized, one end of the coil being electrically connectedto said sleeve, a contact electrically connected to the other end ofsaid coil and carried by said rod for movement therewith, a contact rodarranged for sliding movement within the other end of said tube andarranged initially in electrical engagement with said contact wherebythe coil is energized when said contact rod and said sleeve areconnected across a source of electrical power, a coil spring arrangedwithin the tube to move said actuating rod to said moved positionthereof, a stop member carried by said contact rod and arranged toengage the tube upon limited follow-up movement of the contact rod withrespect to the actuating rod, and a coil spring arranged to yieldablyurge the contact rod into said follow-up engagement with said contactwhereby energization of the coil is maintained until said stop memberengages the tube.

8. A thermal control relay of the character disclosed comprising, incombination, a tube of non-conducting material having an inturned flangeforming an axial opening at one end thereof, a sleeve of conductingmaterial disposed Within said opening and secured to said flange, aconductor ring secured between said sleeve and flange, circuitcontrolling means supported on said tube and including a plurality ofspring contacts arranged in axial alignment with said opening, anactuating rod for said contacts composed of conducting material andarranged for sliding movement within said sleeve, a tube of conductingmaterial sleeved about said rod and arranged in abutting engagement withsaid sleeve, 21 fusible alloy for releasably bonding said rod to saidconducting tube with one end of the rod arranged in spaced relation withrespect to said contacts suflicient to prevent engagement tlierebetweenin response to a shock received by the relay, an electric heat coilmounted on said conducting tube and having one end thereof connectedelectrically thereto, a non-conducting piston connected to the other endof said rod and arranged for sliding movement within said non-conductingtube, a contact carried by said piston in axial alignment with said rodand electrically connected to the other end of said coil, a conductingcap secured to the other end of said non-conducting tube and having aninwardly extending hub portion, a contact ring secured between said capand said non-conducting tube, said hub portion having a central bore inaxial alignment with said rod, a contact rod arranged for slidingmovement within said central bore and initially arranged with one endthereof in electrical engagement with said piston contact thereby tocomplete a circuit for energizing said coil when said contact rings areconnected to a source of electrical energy, a coil spring sleeved aboutsaid hub portion between said piston and said cap for moving said rod toengage and actuate said plurality of contacts when the coil has beenenergized sufliciently to diffuse said bond,

a coil spring sleeved on said contact rod and arranged to yieldably urgethe contact rod into follow-up engagement with said piston contactduring initial movement of the actuating rod, and a stop member carriedby the other end of said contact rod and arranged to engage said cap tostop said follow-up movement of the contact rod following said initialmovement of the actuating rod thereby to interrupt said circuit to thecoil.

9. A thermal control relay for operating the control circuits of amarine mine comprising, in combination, a tube of non-conductingmaterial having an inturned flange portion forming an axial opening onone end thereof, a conducting cap secured to the other end of said tubeand having a central bore in alignment with said opening, a metallic pinslidably arranged Within said bore, means for yieldably urging said pininwardly of said tube, a nonconducting piston slidably arranged withinsaid tube, a metallic extension secured to said piston and initiallyabutting said pin to form an electrical connection therebetween, aconducting rod secured to said piston and slidably arranged within saidtube opening, means for yieldably urging said extension out of abuttingengagement with said pin and said rod outwardly of the tube, a metallicsleeve arranged about said rod and arranged in abutting engagement withthe flange portion of the tube, a fusible alloy for releasably bondingsaid sleeve to said rod, an electroresponsive heating coil mounted uponsaid sleeve in heat transfer relation therewith and having one endthereof connected to said extension and the other end connected to saidsleeve whereby the coil is energized through said extension and pin whensaid cap and sleeve are connected to a source of power thereby torelease the rod from the sleeve for said sliding movement thereof, astop member carried by said pin and disposed outwardly of the cap, meansfor yieldably urging said pin into engagement with said extension andsaid stop member into engagement with the cap thereby to disengage saidpin from the extension to deenergize the coil upon further movement ofthe extension with the rod, and a plurality of circuit control elementsincluded in said mine circuits and normally spaced from said rodsuificiently to prevent engagement therewith in response to a shockreceived by the mine, said circuit control elements being adapted to beoperated by said rod during said further movement of the extension androd.

10. A thermal control relay of the character disclosed comprising, incombination, a non-conducting tube, a plu rality of spring contactssupported on said tube and having the contact elements thereof arrangedcoaxially of the tube, an actuating rod for said contact springsslidably supported in one end of said tube and arranged in spacedrelation with respect to the contact springs suflicient to preventengagement of the contact springs therewith in response to a shockreceived by the relay, means including a fusible bond for releasablylocking said rod in said spaced relation with respect to the contactsprings, a conducting sleeve on said rod, a heater coil mounted on saidsleeve in heat transfer relation with respect thereto for diffusing andbreaking said bond when the coil is energized, one end of the coil beingelectrically connected to said sleeve, a contact electrically connectedto the other end of said coil and carried by said rod for movementtherewith, a contact rod arranged for sliding movement within the otherend of said tube and arranged initially in electrical engagement withsaid contact whereby the coil is energized when said contact rod andsaid sleeve are connected across a source of electrical power, a coilspring arranged within the tube to move said actuating rod to actuatesaid contact springs when the rod is released, a stop member carried bysaid contact rod and arranged to engage the tube upon limited follow-upmovement of the contact rod with respect to the actuating rod, and acoil spring arranged to yieldably urge the contact rod into saidfollow-up engagement with said contact whereby energiz-ation of the coilis maintained until said stop member engages the tube.

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